U.S. Pat. No. 3,905,798 discloses several nitrogen containing monocyclic compounds in the form of quaternary ammonium salts which are useful as plant growth regulators. Of particular interest among such compounds is N,N-dimethylpiperidinium chloride. This compound has demonstrated excellent growth regulator activity on cotton. In discussing this and similar compounds, Jung, in Chapter 16 of "Plant Regulation and World Agriculture" 279-307 (1980, Plenum Press, New York), notes that very slight structural modifications to such compounds can totally destroy the growth regulator activity. Indeed, Jung points out that of a very large number of quaternary ammonium compounds evaluated, several demonstrated a complete lack of activity.
Since the structure-activity relationship among quaternary ammonium salts of the type described above is known to be quite specific and narrow, it is surprising to find that compounds differing rather substantially in structure display comparable growth regulator activity. It has now been discovered that a group of nitrogen containing bicyclic quaternary ammonium salts demonstrate excellent plant growth regulator activity.
Among the compounds which are the subject of this invention are a group of conidinium quaternary salts. Conidine is the name given to a 4,6-bicyclic ring system containing a single bridgehead nitrogen atom. Conidinium quaternary salts were first prepared by Loffler et al. in 1907, Ber., 40, 1310 (1907), and later by Lavagnino et al., J. Am. Chem. Soc., 82, 2609 (1960). Lavagnino et al. additionally describes the preparation of octahydropyrrocoline, the quaternary ammonium salts of which are also useful in the method of this invention.
Quinuclidine is similar to conidine in that it is a nitrogen containing bicyclic ring system. It differs structurally in being a 6,6-bicyclic system rather than a 4,6-system. Like the conidine series, quinuclidine and quaternary ammonium salts of quinuclidine are well known in the art.
The use of bicyclic quaternary ammonium salts such as quinuclidine salts and conidinium salts as plant growth regulators is heretofore unknown. This invention provides a method of controlling vegetative growth employing these bicyclic compounds.